It's one of science fiction's greatest unfulfilled promises, right up there with teleportation and time travel.

And, no, Terrafugia hasn't built us a Tardis or promised to beam us up. But they say they're closer than ever to giving us a flying car.

This week, the Woburn, Massachussetts-based aerospace company announced it has begun feasibility studies on a car capable of vertical takeoffs and landings. The TF-X would be a four-seat, plug-in hybrid electric vehicle, according to the company.

“We are passionate about continuing to lead the creation of a flying car industry and are dedicating resources to lay the foundations for our vision of personal transportation,” Terrafugia CEO Carl Dietrich said in a media release. “Terrafugia is about increasing the level of safety, simplicity, and convenience of aviation. TF-X is an opportunity to provide the world with a new dimension of personal freedom!”

The new TF-X project comes as work on the Transition shifts "from research and development to certification, production, and customer support activities," the company said.

Terrafugia says it has about 100 orders for the Transition, which goes for $279,000.

The big difference between the Transition, which is scheduled to hit the market in 2015, and the new flying car is that the TF-X would be able to take off anywhere, like a helicopter, and not just at an airport.